At present, data communication using Wireless Local Area Networks (WLANs) has already been very popular and global demands for WLAN coverage ever increase. Industrial specification IEEE802.11 group of the Institute of Electrical and Electronics Engineers successively defines a series of standards such as 802.11a/b/g/n/ac to satisfy continuously increasing communication demands.
As illustrated in FIG. 1, in a common WLAN, an Access Point (AP) and a plurality of Stations (STA) associated with it may form a Basic Service Set (BSS). At present, 802.11 supports two methods for judging whether a channel is idle, i.e., physical carrier detection and virtual carrier detection, respectively. Physical carrier detection refers to a Clear Channel Assessment (CCA) channel detection technology, and an associated station judges whether a channel is busy or idle by detecting signal strength on a medium. On a basic bandwidth such as a 20 MHz channel, when it is judged that a received signal is an 802.11 signal and the strength is greater than −82 dBm, it is considered that this channel is busy. Virtual carrier detection refers to that, a third-party associated station except two parties of communication, when receiving a radio frame of which a receiving address is not an address of the third-party associated station itself, sets a local channel protection appointment time according to a transmission time indication in the frame. Transmission time in the frame may be a value of a local Network Allocation Vector (NAV) or a value of a BSS Response Indication Delay counter (BSS RID counter). When the value of the NAV or the value of the BSS RID counter is not zero, it is considered that the channel is busy and contention for transmission is not performed. Only when it is judged that the channel is idle through both physical carrier detection and virtual carrier detection, the associated station can perform contention for accessing to the channel for transmission.
The CCA channel detection technology always uses a fixed threshold as a standard for judging whether a channel is busy or idle, and this decreases access opportunities of the channel in certain scenarios. For example, as illustrated in FIG. 2, station 1 and station 2 are respectively two transmitting stations and can mutually hear signals each other, and a receiving power is greater than the CCA detection threshold (−82 dBm). When a fixed threshold is used for judging whether a channel is busy or idle and when station 1 transmits data to station 3, receiving strength of the signal which is transmitted to station 2 is greater than the CCA detection threshold (−82 dBm) of station 2, and thus station 2 judges that the channel is busy, keeps off and waits. Similarly, when station 2 transmits data to station 4, station 1 can only keep off and wait. Thereby, at each moment, only a pair of stations performs communication. However, in fact, the operation that station 1 transmits data to station 3 does not influence the operation that station 2 transmits data to station 4. Apparently, if the CCA detection threshold is too low and fixed, transmitting opportunities of transmitting stations are decreased and consequently the network utilization ratio is low.
Dynamic Sensitivity Control (DSC) technology can improve channel reusing ratio by dynamically and flexibly configuring the CCA threshold. For example, by properly increasing the CCA detection threshold at proper time, transmitting opportunities can be increased. However, in actual environments, transmitting powers of transmitting stations are different, inequivalent powers of transmitting stations will cause asymmetry of coverage ranges, consequently high-power devices will cause interferences with low-power devices when the CCA threshold is adjusted by using the DSC technology, or unfair contention will be caused. As illustrated in FIG. 3, station 1 and station 2 are transmitting stations and a transmitting power of station 2 is less than a transmitting power of station 1. When station 2 transmits data to station 4, a power of a signal which arrives at station 1 is slightly higher than −82 dBm. At this moment, since station 1 uses the DSC technology to increase the CCA threshold, station 1 judges that the channel is idle and thus the channel is reused to transmit data to station 3. Since the power of station 1 is too high, a serious interference is caused with receiving of station 4 (receiving data of station 2) in a transmission process, consequently the receiving of station 4 (receiving data of station 2) fails. This is the problem of interferences caused by the high-power devices. Similarly, during contention for the channel, station 1 monitors that signal strength of station 2 is low, the DSC technology may be used to increase the CCA threshold and the channel is reused to transmit data to station 3. However, station 2 monitors that signal strength of station 1 is high and exceeds the dynamic adjustment range of the CCA threshold, thus station 2 cannot multiplex the channel to transmit data. This is the problem of unfair contention caused by the high-power devices. No effective solution has already been provided to solve the problems of interference and unfair contention caused by inequivalent transmitting power.